It is proposed to study by single-crystal X-ray analysis, the unknown molecular structures of compounds showing anti-leukemic and anti-tumor activity. These materials will be isolated from plant sources by Professor S. M. Kupchan and his associates. The analyses will be carried out by both the heavy-atom and the direct methods approach to the phase problem, and precise definition of molecular dimensions and stereochemistry is sought. Specific problems to be attacked include the structure determinations of desacetyl hirtin, dehydroeriolanin and dehydroeriolangin, congeners of maytansine, relatives of datiscoside, eupaserrin, and triptenine. A knowledge of the molecular structure of these new and uncharacterized compounds is essential to fully exploit their potential usefulness.